(fx+ 1 2)
=> 3
(fx+ 1 -2)
=> -1
(fx+ -1 2)
=> 1
(fx+ -1 -2)
=> -3
(fx+ 536870911 -1)
=> 536870910
(fx+ 536870910 1)
=> 536870911
(fx+ -536870912 1)
=> -536870911
(fx+ -536870911 -1)
=> -536870912
(fx+ 536870911 -536870912)
=> -1
(fx+ 1 (fx+ 2 3))
=> 6
(fx+ 1 (fx+ 2 -3))
=> 0
(fx+ 1 (fx+ -2 3))
=> 2
(fx+ 1 (fx+ -2 -3))
=> -4
(fx+ -1 (fx+ 2 3))
=> 4
(fx+ -1 (fx+ 2 -3))
=> -2
(fx+ -1 (fx+ -2 3))
=> 0
(fx+ -1 (fx+ -2 -3))
=> -6
(fx+ (fx+ 1 2) 3)
=> 6
(fx+ (fx+ 1 2) -3)
=> 0
(fx+ (fx+ 1 -2) 3)
=> 2
(fx+ (fx+ 1 -2) -3)
=> -4
(fx+ (fx+ -1 2) 3)
=> 4
(fx+ (fx+ -1 2) -3)
=> -2
(fx+ (fx+ -1 -2) 3)
=> 0
(fx+ (fx+ -1 -2) -3)
=> -6
(fx+ (fx+ (fx+ (fx+ (fx+ (fx+ (fx+ (fx+ 1 2) 3) 4) 5) 6) 7) 8) 9)
=> 45
(fx+ 1 (fx+ 2 (fx+ 3 (fx+ 4 (fx+ 5 (fx+ 6 (fx+ 7 (fx+ 8 9))))))))
=> 45